The objectives of this project are to define and generate filarial and strongyloides proteins that are important in inducing parasite-specific immune responses in the human host and to understand, at a molecular level, the differences among related helminth species. Using a variety of techniques including RNA-sparing methods for library construction and splice leader-based PCR, cDNA libraries from a majority of stages and from a majority of filarial parasites of medical importance (W. bancrofti, B. malayi, O. volvulus, L. loa) as well as from both the filariform and rhabdiform larvae of S. stercoralis have been constructed and made available for use. Recombinant antigens and probes have been identified that: a) encode immunoreactive and potentially protective molecules of W. bancrofti; b) can distinguish among related filarial species; c) identify repeated segments of the filarial and non-filarial helminth parasites; and d) are responsible for the induction of immediate hypersensitivity responses in filarial infections.